Liquid sample analysis devices using an immunochromatographic method have been widely used for analyzing liquid samples such as blood of living bodies. FIG. 2 shows an example of a test piece for analysis using the immunochromatographic method. FIG. 2(a) is a plan view (top view) and FIG. 2(b) is a sectional view. In a test piece 1, a sample adding portion 3 and a sample developing layer 4 are formed on a substrate 2. A liquid sample such as blood is added to the sample adding portion 3 by dropping or the like and the added liquid sample is developed in the sample developing layer 4. Further, an antibody reagent 5 is retained at the center of the sample developing layer 4 in the longitudinal direction or on the downstream side of the test piece 1 (hereinafter, a side where the sample adding portion 3 is provided on a longitudinal end of the test piece 1 will be called the upstream side and the other side will be called the downstream side), and a dye labeling reagent 6 that binds to a specific antigen to be measured in the liquid sample is retained upstream of the sample developing layer 4. The sample adding portion 3 is formed by a clearance between the substrate 2 and a cover member 7. The sample developing layer 4 is composed of a nonwoven fabric or a porous material. On the surface of the sample developing layer 4, a protective member such as a transparent sheet (not shown) may be bonded to prevent drying of the liquid sample during the development of the sample.
In analysis, the liquid sample (not shown) added to the sample adding portion 3 of the test piece 1 fills the sample adding portion 3 and then reaches the upstream end of the sample developing layer 4 provided downstream of the sample adding portion 3. The liquid sample at the sample developing layer 4 dissolves the dye labeling reagent 6 retained upstream of the sample developing layer 4 and the dye labeling reagent 6 binds to the specific antigen in the liquid sample. The liquid sample having reacted with the dye labeling reagent 6 further flows downstream through the sample developing layer 4 by capillarity and reaches the antibody reagent 5, so that the antibody reagent 5 captures the specific antigen in the liquid sample by an antigen-antibody reaction. The dye labeling reagent 6 has bound to the captured antigen and thus coloration occurs in a region where the antibody reagent 5 is retained on the sample developing layer 4, according to the concentration of the specific antigen in the liquid sample.
The concentration of the specific antigen in the liquid sample can be measured by optically detecting the coloration. Optical detection methods include a method of irradiating the test piece 1 with laser light and detecting scattered light from the test piece 1 with a photodiode, and a method of imaging the test piece 1 with an image sensor and determining absorbance by image processing on the obtained image. Various liquid sample analysis devices have been proposed using these methods.
In the case where blood is used as a liquid sample without undergoing pretreatment such as cytapheresis, the blood contains solid matters, e.g., blood cell components such as red blood cells and thus the liquid sample (blood) flowing as it is through the sample developing layer 4 may cause the blood cell components to clog at the fibers of the nonwoven fabric or the holes of the porous material, so that the liquid sample may not be normally developed. In order to minimize the occurrence of such a problem, a method has been used in which the sample adding portion 3 contains a blood cell constrictor 8. In this method, the blood cell components in the liquid sample (blood) added by dropping or the like are constricted and then the liquid sample is passed through the sample developing layer 4 (e.g., patent document 1).
In FIG. 3(a), the liquid sample added to the sample adding portion 3 is analyzed while the test piece 1 is held in horizontal position. In this case, the velocity of the liquid sample traveling in the sample developing layer 4 varies depending on the viscosity of the liquid sample, causing variations in the quantity of a liquid sample passing through, in a predetermined time, the retaining portion of the antibody reagent 5 on the sample developing layer 4. Thus an error occurs in analysis results. Moreover, when the liquid sample has an extremely high viscosity, the liquid sample may not reach, within the predetermined time, the retaining portion of the antibody reagent 5 on the sample developing layer 4.
In FIG. 3(b), the liquid sample added to the sample adding portion 3 is analyzed while the test piece 1 is held in vertical position such that the upstream side of the sample developing layer 4 is placed upward along the vertical direction. In this case, the liquid sample added to the sample adding portion 3 flows into the sample developing layer 4 by a gravitational force before the blood cell constrictor 8 retained in the sample adding portion 3 sufficiently dissolves. Thus the liquid sample may not be normally developed to the downstream side of the sample developing layer 4.
To address this problem, the inventors of the present invention have devised a liquid sample analysis device that stabilizes the developing velocity of a liquid sample and a mixed state of the liquid sample and a reagent by changing the orientation of the test piece 1 with respect to the direction of gravitational force after the sample is added.
FIG. 4 shows an example of the configuration of the devised liquid sample analysis device according to the related art. FIG. 4(a) is a perspective view showing a state at the addition of the liquid sample. FIG. 4(b) is a perspective view showing a state at the development of the sample.
In FIG. 4, reference numeral 1 denotes the test piece, reference numeral 11 denotes a holder part that holds the test piece 1, reference numeral 12 denotes a motor (rotating device) for rotating the holder part 11, and reference numeral 20 denotes an optical system for imaging the colored portion (the retaining portion of the antibody reagent 5) of the test piece 1. In the optical system 20, reference numeral 21 denotes a lens, reference numeral 22 denotes an image sensor, and reference numeral 23 denotes a light source that illuminates the surface of the test piece 1. The optical system 20 forms an image of the colored portion (the antibody reagent 5) of the test piece 1 on the imaging surface of the image sensor 22 through the lens 21.
In analysis, as shown in FIG. 4(a), the test piece 1 is first held in horizontal position and the liquid sample (blood) is added (dropped) to the sample adding portion 3. The sample adding portion 3 contains the blood cell constrictor 8 that is dissolved by the added liquid sample and is mixed with the liquid sample, so that blood cell components in the liquid sample (blood) are constricted. When blood cells are constricted after a lapse of a predetermined time, the motor 12 rotates the holder part 11 such that the upstream side of the test piece 1 is placed upward along the vertical direction as shown in FIG. 4(b). Thus the liquid sample containing the blood cells having been sufficiently constricted by the blood cell constrictor 8 flows toward the downstream side of the sample developing layer 4. In this case, the liquid sample simultaneously receives a capillary force generated by the sample developing layer 4 and a gravitational force applied to the downstream side of the sample developing layer 4, thereby stabilizing the developing speed of the liquid sample. Even when the liquid sample has a high viscosity, the liquid sample can develop to the retaining portion of the antibody reagent 5 within the predetermined time.
Citation List
    Patent Literature    Patent Literature 1: Japanese Patent No. 3655283